This invention relates to methods of producing liquid fuels used for transportation engines, and more particularly to a method for producing oxygenated gasoline and diesel fuels.
Recent studies have shown that adding oxygenates to conventional diesel fuel results in substantial reduction of particulate emissions. The extent of reduction correlates with the oxygen content of the fuel.
The conventional method of making oxygenated fuel involves adding a compound, or a mixture of compounds, that contains oxygen in its molecular structure. The fuel manufacturer purchases the oxygen-containing compound or mixture and blends it with diesel fuel.
The conventional method of producing oxygenated diesel fuel significantly increases fuel manufacturing costs. The oxygenated materials to be added are generally made from materials that would otherwise be used as fuels. Thus, adding the oxygenates to the fuel also adds the costs of separating their feed stocks from the fuel, manufacturing the oxygenates, and distributing the oxygenates to the costs of diesel fuel production. There are other disadvantages with conventional oxygenated fuels, such as lower volumetric heating value as compared to non oxygenated fuel.
One aspect of the invention is an autoxidation method of producing oxygenated fuel. First, the sulfur is removed from a base fuel. The sulfur-free base fuel is then heated to a temperature in the range of 150-200 degrees centigrade. Oxygen gas is added, using a sparging procedure. Finally, impurities resulting from the above steps are separated from the oxygenated fuel.
An advantage of the invention is that it provides oxygenated diesel fuel from a sulfur-free base diesel fuel. The oxygenated fuel produces lower particulate emissions from diesel engines than non-oxygenated, sulfur-free diesel fuel. It can be used in engines designed to operate on hydrocarbon fuels, without requiring engine modification or adjustment.
As compared to conventional methods of making oxygenated fuels, an advantage of the invention is that the method is less expensive. It does not require the purchase of an oxygenated compound or mixture. It can be implemented with equipment commonly used in the fuel manufacturing industry. It can be made in large quantities at a reasonable cost and in an energy efficient manner. The process may be added to existing refinery processes.
Manufacturing yields are high. The yield of oxygenated diesel fuel from a base fuel is expected to be at least 95% of the original volume of base fuel.
The method produces oxygenated diesel fuel having properties superior to oxygenated fuels made by conventional methods. In particular, it produces fuel with higher volumetric heating value and generally a higher flash point than oxygenated diesel fuels made by conventional methods.